Method for deactivating and recovering boron trifluoride when producing polyisobutenes

ABSTRACT

The invention relates to a method for deactivating and recovering boron trifluoride when producing polyisobutenes by means of cationic polymerization of isobutene or hydrocarbon streams containing isobutene in the liquid phase in the presence of boron trifluoride or in the form of a boron trifluoride catalyst complex. The catalyst complex is separated, essentially in the liquid phase, from the reactor discharge. The method comprises the following steps: a) removing from the polymerization reactor at −60 to 020  C., methanol, ethanol or a mixture of methanol and ethanol in such a quantity that an alcohol phase rich in boron trifluoride is formed; b) separating the alcohol phase according to (a) and, (c) optionally recycling the boron trifluoride of the alcohol phase obtained from (b) to the method in a suitable manner.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for deactivating andrecovering boron trifluoride in the preparation of polyisobutenes bycationic polymerization of isobutene or isobutene-containing hydrocarbonstreams in the liquid phase in the presence of boron trifluoride as suchor in the form of a boron trifluoride catalyst complex, in which thecatalyst complex is separated as a substantially liquid phase from thedischarge from the reactor.

2. Description of the Background

High molecular weight polyisobutenes having weight average molecularweights (M_(w)) of up to several hundred thousand Dalton have long beenknown, and their preparation is described, for example, in H. Guterbock:Polyisobutylen und Mischpolymerisate, Springer Verlag, Berlin 1959 pages77 to 104. The highly reactive polyisobutenes which as a rule haveweight average molecular weights of from 500 to 50000 Dalton and a highcontent of terminal double bonds, i.e. vinylidene groups, preferablysubstantially more than 60 mol %, should be distinguished from theseconventional polyisobutenes.

Such highly reactive polyisobutenes are used as intermediates for thepreparation of additives for lubricants and fuels, as described, forexample, in DE-A 27 02 604. For the preparation of these additives,polyisobutene/maleic anhydride adducts, in particularpolyisobutenylsuccinic anhydrides, are first produced by reacting theterminal double bonds of the polyisobutene with maleic anhydride and arethen reacted with specific amines to give the final additive. Theproportion of terminal vinylidene groups in the molecule is one of themost important quality criteria for this polyisobutene type since, inthe adduct formation with maleic anhydride, mainly the terminalvinylidene groups react whilst, depending on their position in themacromolecule, the double bonds present further toward the interior ofthe macromolecules do not react or react to a substantially smallerextent, without the addition of suitable activators.

The generation of the terminal vinylidene groups and the isomerizationof the terminal double bonds in the isobutene macromolecules to giveinternal double bonds are described, for example, in the article byPuskas et al., J. Polymer Sci.: Symposium No. 56, 191 (1976) or EP-A 628575. The protonations, deprotonations and rearrangement reactions takingplace there are equilibrium reactions in which the formation of morehighly alkyl-substituted cations is thermodynamically favored. Saidreactions are as a rule promoted by traces of acid, in particular by thecatalyst of the polymerization itself, which is usually a Lewis acidcatalyst.

A further quality criterion for polyisobutenes having the said intendeduse is their number average molecular weight (M_(n)). Number averagemolecular weight is a quantity which indicates the average molecularsize present in the product of the polymerization. In general,polyisobutenes having a number average molecular weight of from 200 to50000, preferably from 200 to 5000, in particular from 500 to 3000 andespecially from 500 to 2500, Dalton are used.

The molecular weight distribution (dispersity, D) of the polyisobutenemacromolecules is also a quality criterion for said purpose since, thebroader it is, i.e. the greater the scatter of the molecular weights ofthe polyisobutene macromolecules about a mean value, often the lesstailored are the products to a specific property.

A person skilled in the art is familiar with a number of processes forthe preparation of highly reactive polyisobutenes from isobutene whichhave number average molecular weights and dispersities which meet saidrequirements and for which boron trifluoride is used as a catalyst.

Boron trifluoride is used predominantly in the form of donor complexes,in particular with water, alcohols, phenols, carboxylic acids,carboxylic anhydrides, hydrogen fluoride, ethers or mixtures of thesecompounds. Boron trifluoride, as such or in the form of said complexes,is a catalyst which is extremely effective even at low temperatures (cf.for example DE-A 27 02 604, EP-A 145 235 or EP-A 322 241).

If it is therefore intended to stop the boron trifluoride-catalyzedpolymerization of isobutene after a defined conversion and/or a definedselectivity with respect to the macromolecular products has beenreached, the boron trifluoride must as a rule be rapidly and completelydeactivated. This deactivation may consist in decomposing the borontrifluoride, for example in hydrolyzing it with sodium hydroxidesolution, or in complexing it with stronger donors in order to remove itfrom the reaction.

DE-C 40 33 196 states that the reaction can be stopped with ammonia orwith from 5 to 50% strength by weight aqueous sodium hydroxide solution.However, sodium or ammonium salts which form thereby cannot becompletely separated off from the reaction product polyisobutene, evenby washing several times with water, and present problems in theapplications described above, generally even in amounts of less than 10,often of even less than 0.1 ppm.

According to DE-A 43 06 384, the deactivation of the boron trifluoridecan be carried out using water, alcohols, acetonitrile, ammonia oraqueous solutions of mineral bases, such as alkali metal and alkalineearth metal hydroxide solutions, or with solutions of carbonates ofthese metals.

The hydrolytic processes under aqueous conditions for deactivating theboron trifluoride all lead to waste waters which are problematic owingto their content of inorganic fluoride of course, the boron trifluoridealso cannot be recycled economically for re-use in the process by thismethod. Since the processes of this type for the preparation ofpolyisobutenes generally have to be carried out at low temperatures inorder to be sufficiently selective, the aqueous hydrolysis of thereactor discharge usually has to be carried out with heated water inorder to be sufficiently rapid and complete and to avoid the formationof ice in the discharge. In these generally short heating-up phases,however, undesirable by-products may form, i.e. the overall selectivityof the reaction decreases. Particularly for industrial processes,however, this procedure also means that some of the energy consumed forreaching the low reaction temperature is lost. With the use of water, alarger or smaller amount of corrosive hydrofluoric acid is alsovirtually always formed, necessitating the use of high-quality and henceusually expensive materials, in particular special steels for theconstruction of the downstream parts of the plant.

The deactivation of the boron trifluoride with the aprotic acetonitrile(cf. for example EP-A 145 235) takes place rapidly. However, the toxicacetonitrile is generally used in excess and is readily water-soluble,so that large amounts of problematic waste water result duringworking-up.

WO-A 99/31151 discloses that boron trifluoride can be separated from thereaction mixture of the isobutene polymerization in the form of anisopropanol complex, and the boron trifluoride can be made availableagain for the reaction in this way. In order for this separation to takeplace, not more than 2% by weight of isobutene may be present in thereaction mixture. In practice, however, this content leads to productsof reduced reactivity in the reaction of isobutene to givepolyisobutenes having number average molecular weights of more than1000, so that low isobutene contents are preferably avoided in this wayand in these cases unconsumed isobutene is removed from the reactionmixture at the end of the reaction with considerable additionaltechnical effort.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved processfor deactivating and recovering boron trifluoride from reaction mixturesas obtained in the preparation of highly reactive polyisobutenes fromisobutene with the use of boron trifluoride as a catalyst.

We have found that this object is achieved by a process for deactivatingand recovering boron trifluoride in the preparation of polyisobutenes bycationic polymerization of isobutene or isobutene-containing hydrocarbonstreams in the liquid phase in the presence of boron trifluoride as suchor in the form of a boron trifluoride catalyst complex, the catalystcomplex being separated as a substantially liquid phase from thedischarge from the reactor, wherein

-   -   a) methanol, ethanol or a mixture of methanol and ethanol is        added to the discharge from the polymerization reactor at from        −60 to 0° C. in an amount such that a boron trifluoride-rich        alcohol phase separates out,    -   b) the alcohol phase according to (a) is separated off and    -   c) the boron trifluoride of the alcohol phase according to (b)        is, if desired, recycled to the process in a suitable manner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The use of methanol is particularly advantageous when carrying out thenovel process.

The alcohols methanol, ethanol and their mixtures with one another whichare used according to the invention for deactivating and recoveringboron trifluoride, are referred to herein as alkanols for short.

Here, terminal vinylidene groups or terminal double bonds are understoodas meaning those double bonds whose position in the polyisobutenemacromolecule is described by the formula I

where R is the remaining part of the polyisobutylene macromolecule. Thetype and the amount of the double bonds present can be determined withthe aid of ¹³C-NMR spectroscopy, the two carbon atoms of the terminaldouble bond which are indicated by α and β in the formula I beingidentifiable in the ¹³C-NMR spectrum by their signal at the chemicalshifts of 114.4 and 143.6, respectively, relative to tetramethylsilane.The proportion of terminal double bonds relative to other types ofdouble bonds is determined by expressing the peak areas of theindividual olefin signals in each case as a ratio of the total areaintegral of the olefin signals.

For the preparation of highly reactive polyisobutenes from isobutene inthe presence of boron trifluoride, usually either the required amount ofpreformed boron trifluoride complex solution or suspension is dispersedin the isobutene or alternatively the catalyst is produced in situ bypassing gaseous boron trifluoride into the isobutene and the complexingagent for the boron trifluoride. The catalytically active systemcomprising boron trifluoride and the complexing agent, which is formedby one of said routes, is referred to below as catalyst system.

Suitable complexing agents for the boron trifluoride in the reaction ofisobutene to give highly reactive polyisobutenes are alcohols,preferably secondary alcohols, with for example 1 to 4 carbon atoms andin particular, independently of one another, isopropanol and sec-butanol(cf. EP-A 628 575). A dialkyl ether (cf. U.S. Pat. No. 5,408,018) and inparticular a dialkyl ether which has at least one tertiary alkyl groupor at least one secondary alkyl group can also be added as a furthercomplexing agent to these catalyst systems. Such catalyst systems aredisclosed in WO-A 99/64482, which is hereby wholly incorporated byreference with respect to the catalyst complexes.

In general, the same molar amount, preferably from 2.5 to 1.05, inparticular from 2 to 1.25, times the molar amount, based on borontrifluoride used, of such alcohols and/or ethers as complexing agents ispresent.

Usually, the catalyst system is used in amounts of from 0.05 to 1% byweight, based on the weight of the isobutene used. The gross reactionrate and the molecular weight are dependent as a rule on the amount ofcatalyst system used, but especially on the molar ratio of the catalystused to isobutene used.

Pure isobutene as well as mixtures of isobutene with other hydrocarbonscan be used as isobutene-containing starting material (referred to belowas isobutene feedstock) in the synthesis step preceding the deactivationof the boron trifluoride, the isobutene content of such mixturesexpediently being not less than 5% by weight. Preferably, hydrocarbonmixtures having a high isobutene content and a very low butadienecontent are used, for example refined fraction I, a partiallyhydrogenated C₄ stream from a steam cracker, a C₄ stream from the fluidcatalyst cracking of the refineries or a C₄ stream from an isobutanedehydrogenation.

The isobutene feedstock can be reacted in the presence of the catalystsystem in one or more inert solvents to give the polyisobutene. Suitablesolvents, individually or as a mixture with one another, are saturatedhydrocarbons, for example n-butane, n-pentane, n-hexane, isooctane orcyclohexane, halogenated hydrocarbons, such as methylene chloride,chloroform and other halohydrocarbon compounds having suitable meltingpoints and boiling points. If isobutene-containing hydrocarbon steamsare used as the isobutene feedstock, the hydrocarbons contained thereinwhich are inert under the reaction conditions perform the function ofthe solvent.

The isobutene feedstock may contain small amounts of impurities, such aswater, acetaldehyde, acetone, acetonitrile, carboxylic acids or mineralacids, without there being critical decreases in the yield orselectivity as a result in the polymerization. However it is expedientto avoid an accumulation of these impurities in the reactor by removingthem from the isobutene feedstock beforehand, for example by means ofadsorption onto solid adsorbents, such as active carbon, molecularsieves or ion exchangers.

The polymerization of the isobutene can be carried out batchwise,semibatchwise or continuously. Reactors known per se, such as tubularreactors, tube-bundle reactors or stirred kettles, can be employed forthis purpose. The preparation process is preferably carried out in aloop reactor, i.e. a tubular reactor or tube-bundle reactor withcontinuous circulation of the reaction material, it being possible as arule for the volume ratio of feed to circulation to be from 1:1 to1:1000, preferably from 1:30 to 1:200. Of course, the amount offeedstocks introduced into the reactor corresponds to the amount ofreaction discharge as soon as the polymerization reaction has reached anequilibrium state.

It is expedient to ensure thorough mixing of all reactants both whenintroducing preformed catalyst complexes into the reactor and duringtheir in situ preparation in the reactor, since high local andsteady-state catalyst concentrations in the reactor can give rise toundesirable double bond shifts in the polymeric products. Thoroughmixing is achieved, for example, by suitable internals, such as baffleplates, or by adapted tube cross-sections which, in the case of asuitable flow rate, lead to an effective, expediently turbulent flow ofthe reaction material in the reactor.

The residence time of the isobutene in the reactor may be from 5 secondsto several hours. Preferably a residence time of from 1 to 30,particularly preferably from 2 to 20, minutes is chosen.

The polymerization is generally carried out at below 0° C. Althoughisobutene can be successfully polymerized even at substantially lowertemperatures by means of the catalyst system to give highly reactivepolyisobutene, preferably temperatures of from 0 to −60° C., inparticular from 0 to −30° C., particularly preferably from −5 to −25°C., are employed.

Advantageously, the polymerization reaction is operated under isothermalconditions and, in the case of a continuous reaction, with establishmentof a constant, steady-state isobutene concentration of the reactionmedium. The steady-state isobutene concentration can in principle bechosen as desired. Expediently, an isobutene concentration of, as arule, from 0.2 to 50, preferably from 0.2 to 10, % by weight, based onthe total polymerization mixture, is established.

In general, the polymerization is carried out under atmospheric pressureor pressure slightly higher than atmospheric pressure. The use ofsuperatmospheric pressure, in particular the autogenous pressure of thereaction system, may be advantageous from process engineering points ofview with regard to the operation of the circulation pumps anddownstream process stages but is generally not necessarily required forthe result of the polymerization.

Since the polymerization reaction is exothermic, the resulting heat isremoved as a rule with the aid of a cooling apparatus which can beoperated, for example, with liquid ammonia as a coolant. Anotherpossibility for removing the heat is by evaporative cooling, where theheat evolved is removed by vaporizing the isobutene, other readilyvolatile components of the isobutene feedstock and/or any readilyvolatile solvent, which may be ethane, propane or butane, with theresult that the temperature remains constant.

The isobutene conversion can in principle be established as desired.However, the cost-efficiency of the process is of course questionable atvery low isobutene conversions, whereas the danger of undesirablesecondary reactions, for example of double shifts and especially of theformation of undesirable oligomers, becomes increasingly great at veryhigh isobutene conversions of more than 99%. For these reasons, theisobutene conversion is as a rule from 20 to 99.5%, preferably from 90to 99%. If it is intended to obtain polyisobutenes having high molarmasses, the isobutene conversion is as a rule kept low, which generallyleads to a high content of unconsumed isobutene in the reaction mixture.

In the discharge from the reactor (referred to below as discharge forshort), the major part of the boron trifluoride used is as a rulepresent in free form or as a complex with the originally addedcomplexing agent. However, it is not possible to rule out thepossibility that a reaction of the boron trifluoride with othercomponents of the reaction mixture has taken place, for example, withthe use of isopropanol as a complexing agent, to give a borane. Owing tothe usually small extent of such secondary reactions, however, they willnot be considered further here, especially since the boranes formed withprotic compounds are highly soluble in the organic phase and are verysubstantially destroyed in the aqueous washing of the polyisobutene.Rather, for the sake of simplicity and as a good approximation to theactual circumstances, it is to be assumed that all the boron trifluorideused is still intact as such at the time of the deactivation accordingto the invention.

The deactivation and recovery of the boron trifluoride can in principlebe carried out batchwise, semibatchwise or continuously. Preferably, thedeactivation and removal are carried out at from −30 to 0° C., inparticular from −25 to −5° C. If the polymerization of the isobutenewith boron trifluoride is carried out continuously, the borontrifluoride in the discharge is preferably deactivated continuously withthe alkanols.

The alkanols can also be diluted, before the deactivation, with one ormore further solvents inert under the reaction conditions and especiallynonpolar, such as hydrocarbons or halogenated hydrocarbons, preferablythose having a boiling point below 100° C., e.g. n-pentane, n-hexane, ordichloromethane. Such solvents can also be added to the dischargedirectly as such during the deactivation. In the mixtures with the inertsolvents, the alkanols are generally present in an amount of from 5 to100, preferably more than 20, % by weight.

The alkanols are used in a molar ratio of from 1:1 to 20:1, especiallyfrom 2:1 to 15:1, and in particular from 2:1 to 10:1, based on the borontrifluoride present in the discharge. For economic reasons, as far aspossible only a small excess of the alkanols is used, but the greaterthe excess thereof or the better the mixing the more rapidly andcompletely the deactivation generally takes place. Since a rapid andcomplete deactivation of the boron trifluoride is an importantprecondition for ensuring that the product composition reached in thepolymerization in the reactor no longer changes substantially by the endof the working-up, the use of a larger excess of alkanols may beadvisable.

For the purpose of deactivating the boron trifluoride, the alkanols areintroduced into the discharge and vigorously mixed with it, or they areinitially taken and the discharge is added to them with vigorous mixing.

The resulting boron trifluoride complex is as a rule poorly soluble inthe reaction medium and, at the temperature of the deactivation, usuallyforms a second phase which can be separated off in a simple manner andwhose boron trifluoride content is in general greater than 10,preferably 20, especially 25, % by weight. Such a separationsurprisingly also occurs at high residual contents of isobutene in thedischarge of, in particular, more than 2% by weight, for example, in thepreparation of polyisobutenes having an M_(n) of from 1000 to 5000Dalton.

In a further embodiment of the novel process, water can be added to thedischarge for deactivating the boron trifluoride, in addition to thealkanol. The amount of water is up to 70, preferably up to 60, inparticular from 5 to 50, % by weight, based on the alkanols, and, ifrequired, mixtures thereof with solvents. Preferably, the water is notadded until after the alkanols have first been allowed to act on theboron trifluoride in the discharge and after the mixture thusobtained—for example by means of a heat exchanger for recovering thecooling energy—has reached a temperature above the temperature at whichthe water in the mixture would freeze. This temperature is as a ruleabove 0° C.

In a further embodiment, alkanol and water are added together to thedischarge.

Apparatuses which ensure rapid and complete mixing are preferably usedin the deactivation of the boron trifluoride. For example, stirredkettles and preferably static mixers are used. Since hydrogen fluoridecan form from boron trifluoride in the presence of, in particular,water, it may be necessary to avoid any contact of the reaction mixturewith materials which are not resistant to hydrogen fluoride, such asglass or enamel.

The deactivation of the boron trifluoride is preferably carried out atthe temperature of the polymerization, especially at from 0 to −30° C.,in particular from 0 to −25° C. Deactivation at a temperature other thanthe reaction temperature is also possible; during the temperatureincrease or reduction required for this purpose, however, the reactionproduct may change in an undesirable manner as described above.

After the total amounts of the discharge, of the alkanol or, ifrequired, of an alkanol/water mixture have been combined, the mixtureobtained is usually kept thoroughly mixed for a further 10 seconds to 20minutes using suitable apparatuses, for example with conventionalmechanical stirrers and, in particular, by means of turbulent flow.

The formation of in particular two phases, one of which contains themain amount of the deactivated boron trifluoride (borontrifluoride/alkanol phase) and the other contains the main amount of thepolyisobutene (organic phase), is particularly advantageous for thefurther working-up of the mixture thus obtained.

Such a phase separation can as a rule be substantially further improvedin specific situations, for example at very high residual contents ofisobutene in the discharge, if water is added to the discharge. Thespecific amount of water to be added can easily be determined by a fewsmall-scale experiments by a person skilled in the art.

In addition to the main amount of the polyisobutene, the organic phasefurthermore usually comprises the unconverted isobutene, low molecularweight polymers of isobutene, in particular having number averagemolecular weights below 300 Dalton, and, if required, the solvent.

Small residual amounts of boron trifluoride can be removed from theorganic phase, if desired also by extraction, for example with methanol,or preferably by washing with water.

In the further course of the working-up, the organic phase isexpediently separated by distillation into unconverted isobutene, anysolvent, the low molecular weight polymers of isobutene and the desiredproduct polyisobutene. The isobutene, the solvent and the low molecularweight polymers can be recycled to the polymerization independently ofone another or together. The desired polyisobutene is as a rule taken upas a bottom product from the distillation column or a degassing tank.

The boron trifluoride/alkanol phase can be recycled as such to thereactor. It should be ensured that no undesirable dilution or viscosityreduction of the reactor content by the alkanol occurs. Moreover, thefact that methanol and ethanol may replace the alcohol which is part ofthe catalyst system should be taken into account. Correspondingconcentration operations and, if desired, purification operations are asa rule therefore first preferably carried out on the borontrifluoride/alkanol phase before it is recycled to the process.

The concentration of the boron trifluoride in the phase separated offaccording to the invention can be effected in various ways. Thus,organic components, for example excess alkanols, can be distilled off bymeans of simple distillation from the boron trifluoride-containing phaseseparated off according to the invention. At first the boron trifluorideremains there in the bottom and, for example when the alkanol used ismethanol, can be concentrated to more than 50% by weight.

Alternatively, the boron trifluoride/alkanol complex can be isolated,for example by freezing. BF₃. 2 MeOH has, for example, a freezing pointof −20° C.

In another method for working up the boron trifluoride/alkanol phase,water is first added to said phase and then the organic components, suchas methanol, ethanol, any solvent and organic components of theoriginally used catalyst complex, and any excess water are removed bymeans of distillation or steam stripping. In this way, a borontrifluoride concentration of more than 50% by weight can be achieved inthe residue. The boron trifluoride/water phase thus obtained is usuallyvirtually free of organic components and is thermally comparativelystable, which is advantageous for storage and transport thereof. Gaseousboron trifluoride of very high purity can therefore be liberated from itin a very simple manner known per se to a person skilled in the art, forexample with the aid of oleum.

We have furthermore found that the presence of methyl tert-butyl ether(abbreviated to MTBE below) or, with the use of ethanol, also thepresence of ethyl tert-butyl ether in the reaction mixture of the borontrifluoride-catalyzed preparation of polyisobutenes leads to an improvedselectivity with respect to the terminal group character of thepolyisobutenes prepared. As a rule, the terminal group character can beimproved by up to 10% in this way. The amount of these ethers in thereaction mixture is in general from 20 to 5000, preferably from 30 to3000, in particular from 40 to 2000, ppm (based on the total weight ofthe reaction mixture). If such an ether can also form in the reactionmixture, it is expedient to consider its initial concentration in thereaction zone, which can be derived in practice from its added amount,and its concentration in the discharge.

With the use of methanol as the alkanol in the context of the presentinvention, MTBE may form under specific conditions in the reactionmixture, on termination or at elevated temperatures in the heatexchanger. Investigations carried out have shown that the amount of MTBEformed in the preparation process for the polyisobutene is closelycorrelated with a molar methanol:boron trifluoride ratio under otherwisevirtually comparable reaction conditions. Thus, at a molar ratio of from0.3:1 to 20:1, and in particular from 15:1 to 1:1, MTBE formation takesplace simultaneously with the deactivation of the catalyst complex, itbeing observed that the amount of MTBE formed per unit time decreaseswith increasing amount of ethanol.

We have also found that the formation of the MTBE in a reaction mixturein which in general tert-butyl cations and methanol form asintermediates and/or are present can also be controlled by the choice ofthe solvent, of the reaction temperature, of the residence time of thereaction mixture and the reaction zone and of the isobuteneconcentration there. This means that a person skilled in the art canroutinely and readily establish the respective desired amount of MTBE bycorresponding adaptation of the composition of the reaction mixture, ofthe procedure and of the apparatuses used—of course under the conditionsof the polymerization process for isobutene.

During the working up of the discharge, MTBE or ethyl tert-butyl etheris then recycled in the desired amount to the process in a manner knownper se, for example together with the catalyst complex or together withthose reuseable components of the reaction mixture which have beenseparated off by distillation, such as isobutene, or together with thesolvent.

By means of the novel process, the desired polyisobutenes can beprepared in higher yields and with higher vinylidene contents than byconventional processes of this type.

Because the hydrolysis of the boron trifluoride to hydrofluoric acid andderivatives of boric acid does not play any significant role in thenovel procedure, corrosion of plant parts occurs only to a minor extent.

EXAMPLES

The number average molecular weights (M_(n)) of the polymers preparedaccording to the examples were determined by means of gel permeationchromatography, polyisobutenes having defined known values M_(n) beingused for the calibration. The chromatograms obtained were used tocalculate M_(n) according to the equation$M_{n} = \frac{\sum C_{i}}{\sum\frac{C_{i}}{M_{i}}}$where C_(i) is the concentration of an individual polymer species i inthe polymer mixture obtained and Mi is the molecular weight of thisindividual polymer species i.

The dispersity D was calculated from the ratio of weight averagemolecular weight (M_(w)) to number average molecular weight [lacuna]according to the equation $D = {\frac{M_{w}}{M_{n}}.}$

The weight average molecular weight M_(w) required for this purpose wasobtained from the resulting chromatograms with the aid of the formula$M_{w} = {\frac{\sum{CiMi}}{\sum C_{i}}.}$

The content of terminal vinylidene groups was determined with the aid of¹³C-NMR spectroscopy, deuterated chloroform being used as the solventand tetramethylsilane as the standard.

Example 1 Preparation of Highly Reactive Polyisobutene

For the preparation of a polyisobutene, the procedure according to EP-A628 575, Example 1, was followed: the isobutene feedstock used was aC₄-cut having the following composition:

isobutane   4.0% by weight n-butane   9.2% by weight 1-butene  29.0% byweight trans-2-butene   7.7% by weight cis-2-butene   4.5% by weightisobutene  45.4% by weight butadiene   <50 ppm water about 2 ppm

In the course of one hour, 6000 g of the above C₄-cut were fed to thesuction side of a loop reactor which was equipped with an integratedcirculation pump and whose internal tube diameter was 4 mm and whosevolume was 1000 ml. 1.6 times the molar amount of 2-butanol, based onthe boron trifluoride, were added. The reactor was cooled so that thetemperature in the reaction medium was −17° C. The average residencetime of the reaction medium of the reactor was 6.6 minutes. Samples ofthe reactor content were taken via a sampling apparatus which waslocated 2 cm before the feed for the starting materials.

Examples 2 to 8 Continuous Deactivation and Removal of the BoronTrifluoride

Methanol was initially taken in a closable, pressure-resistant glasssampling bottle, and a 70 ml sample according to Example 1 was added inthe course of a few seconds at −17° C. with thorough mixing. The mixturewas heated from −17 to 20° C. in the closed glass sampling bottle in thecourse of 30 minutes while stirring by means of a magnetic stirrer. Thestirrer was then switched off, after which droplets of a second phasewere visible. The main amount of the boron trifluoride was present inthe droplets (as the lower phase), which were separated off. Theremaining organic phase was thoroughly mixed with 167 g of water for 60minutes with stirring. After the aqueous phase had been separated off,the solvent was distilled off, and the analytical data listed in Table 1were determined for the residue of the distillation.

TABLE 1 Further data for examples 2 to 8 Methanol BF₃ Amount Amount No.[mmol/l] [g] [mmol] Water [g]* C [%] Y [%] Vin [%] M_(n) D 2 7.1 1 31 —94 93 85.6 2831 1.741 3 7.1 0.2 6.3 — 95 93 85.4 2844 1.788 4 7.1 0.13.1 — 94 93 86.0 2849 1.788 5 7.1 0.05 1.6 — 94 93 85.6 2855 1.793 6 7.10.02 0.6 — 94 93 85.2 2773 1.835 7 7.1 0.5 15.6 0.5 94 93 85.2 27931.729 8 7.1 0.3 9.4 0.7 94 93 85.4 2777 1.802 *Water was addedsimultaneously with the methanol

In table 1, the meanings are as follows:

-   -   BF₃ content of BF₃ in the sample: the amount of BF₃ added to the        reaction was taken as a basis (see above)    -   C conversion in percent, based on isobutene used    -   Y yield of polyisobutene, based on isobutene used    -   Vin proportion of polyisobutene having vinylidene double bonds,        based on the total polyisobutene yield    -   M_(n) number average molecular weight (determined by gel        permeation chromatography)    -   D dispersity

Examples 9 to 13 Continuous Deactivation and Removal of the BoronTrifluoride

An isobutene feedstock having the following composition was polymerizedaccording to Example 1:

isobutane, <1% by weight n-butane, 1-butene, trans-2-butene andcis-2-butene together 1-butene <1% by weight trans-2-butene <1% byweight cis-2-butene <1% by weight isobutene 45% by weight butadiene <50ppm water about 2 ppm n-hexane remainder to 100% by weight.

However, in contrast to Example 1, 1.6 times the molar amount of2-propanol, based on the boron trifluoride, were added and the reactorwas cooled so that the temperature in the reaction medium was −19° C.The reactor discharge was passed through a tube which was cooled to −18°C. and to which methanol was added continuously by means of a staticmixing apparatus (nozzle). No temperature increase was observed. In adownstream dwell tank cooled to −17° C. and having a volume of 400 ml,the reactor discharge treated in this manner was separated into twophases, the lower of which contained the predominant part of the borontrifluoride. This lower phase was separated off and the content of borontrifluoride (boron trifluoride recovery) was determined. It was from 43to 73% by weight in the individual samples brought to room temperature.Further data on experiments 9 to 13 are to be found in Table 2 below.

TABLE 2 Further data on Examples 9 to 13 BF₃ recovery in the MTBEcontent in Methanol lower phase [g/h] the discharge [ppm BF₃ BF₃ AmountAmount ([% of amount of the total weight U A Vin N. [mmol/h] [g/h] [g/l][mmol/l] used]) of the discharge] [%] [%] [%] M_(n) D 9 53.3 3.61 20 6252.64 (73) <20 95 94 80.7 2675 1.715 10 53.3 3.61 10 313 2.56 (71) <20 9594 81.3 2651 1.729 11 53.3 3.61 7.5 234 2.64 (73) 27 95 94 83.9 26491.738 12 53.3 3.61 5 156 2.31 (64) 97 95 93 87.3 2655 1.793 13 53.3 3.612.5 78 1.55 (43) 183 95 93 89.7 2473 1.835 For the meanings of theabbreviations used, cf. Table 1

Example 14 Recycling of the Lower Phase from Example 11 to the reactor

The experimental procedure of Example 11 was modified in such a way that3 g per hour of 8.7 g of the lower, boron trifluoride-rich phase (borontrifluoride content 33% by weight) separated off in the same period wererecycled continuously to the reactor. On the other hand, the amount offresh boron trifluoride added was reduced from 53.3 to 38.6 mmol/h, i.e.by 1 g/h. The molar 2-propanol:BF₃ ratio in the reactor was furthermorebrought to 0.5. The reaction and the polyisobutene obtained werecharacterized by:

C 96% Y 94% Vin 86.9% M_(n) 1987   D 1.698   (The abbreviations areexplained in Table 1.)

(The abbreviations are explained in Table 1.)

Example 15 Working-Up of the Lower Phase of Example 11 by distillation

50 ml of the lower phase (boron trifluoride content 33% by weight)obtained according to Example 11 were introduced into a distillationapparatus which consisted of a 100 ml three-necked flask having awater-cooled distillation bridge and provided with thermometer andstirrer. The flask was heated from the outside by means of a heatingjacket. The content of the flask began to boil at 62° C. underatmospheric pressure. The boiling point of the distillate passing overincreased continuously to 105° C. Above 105° C., slight mist formationoccurred. The distillation was then stopped. For the 28 ml (22.1 g) ofdistillate, analysis gave a boron trifluoride content of 1.4% by weight;the residue (22 ml, 27.0 g) had a boron trifluoride content of 59.4% byweight.

Example 16 Working-Up of the Lower Phase of Example 11 by distillationwith Addition of Water

The distillation according to Example 15 was repeated but 15 ml of waterwere added dropwise beforehand to the reactor discharge, the content ofthe distillation flask heating up. The content of the flask began toboil at 62° C. under atmospheric pressure. The boiling point of thedistillate passing over increased continuously to 118° C. Above 118° C.,slight mist formation occurred. The distillation was then stopped. Forthe 40 ml (34.8 g) of distillate, the analysis gave a boron trifluoridecontent of 1.9% by weight; the residue (23 ml, 29.3 g) had a borontrifluoride content of 60.3% by weight and an organic carbon content(TOC) of 237 ppm by weight.

1. A process for deactivating and recovering boron trifluoride in thepreparation of polyisobutenes by cationic polymerization of isobutene orisobutene-containing hydrocarbon streams in the liquid phase in thepresence of boron trifluoride as such or in the form of a borontrifluoride catalyst complex in a reactor, the catalyst complexseparating as a substantially liquid phase from the material dischargedfrom the reactor, comprising: a) adding methanol, ethanol or a mixtureof methanol and ethanol to the material discharged from thepolymerization reactor at a temperature from −60 to 0°C. in an amountwhich results in the formation of a boron trifluoride-rich alcoholphase; b) separating the alcohol phase containing boron trifluoride fromthe material discharged from the reactor; and c) optionally recyclingthe boron trifluoride of the alcohol phase obtained from (b) to theprocess in a suitable manner.
 2. The process as claimed in claim 1,wherein methanol is the alcohol added to process step (a).
 3. Theprocess as claimed in claim 1, wherein the formation of the borontrifluoride-rich alcohol phase in process step (a) is facilitated byadding water to the material discharged from the polymerization reactor.4. The process as claimed in claim 1, wherein the polyisobutene is ahighly active polyisobutene having from 80 to 100 mol % of terminaldouble bonds.
 5. The process as claimed in claim 1, wherein the highlyactive polyisobutene has a number average molecular weight Mn rangingfrom 200 to 50000 Dalton.
 6. The process as claimed in claim 1, whereinthe cationic polymerization is conducted with a catalyst system whichcontains isopropanol.
 7. The process as claimed in claim 1, wherein thecationic polymerization is conducted with a catalyst system whichcontains methanol.
 8. The process as claimed in claim 6, wherein thecationic polymerization is conducted with a catalyst system whichfurther comprises a dialkyl ether having at least one secondary alkylgroup.
 9. The process as claimed in claim 1, wherein the deactivationand recovery of the boron trifluoride are conducted continuously. 10.The process as claimed in claim 1, wherein the polymerization ofisobutene is conducted in the presence of from 20 to 5000 ppm of methyltert-butyl ether, based on the weight of the reaction mixture.
 11. Theprocess as claimed in claim 10, in which the methyl tert-butyl ether isformed at least partially in the process.
 12. The process as claimed inclaim 10, wherein the methyl tert-butyl ether in the material dischargedfrom the reactor is separated and is partially or fully recycled to theprocess.
 13. The process as claimed in claim 7, wherein the cationicpolymerization is conducted with a catalyst system which furthercomprises a dialkyl ether having at least one secondary alkyl group. 14.The process as claimed in claim 12, wherein the methyl tert-butyl etherin the material discharged from the reactor is separated and ispartially or fully recycled to the process.
 15. The process as claimedin claim 1, wherein the boron trifluoride catalyst is a complex of borontrifluoride with an alcohol or a dialkyl ether that has at least onetert-alkyl group, in a molar ratio of complexing agent to borontrifluoride of 2.5 to 1.05:1.
 16. The process as claimed in claim 15,wherein the boron trifluoride catalyst is a complex of boron trifluoridewith an alcohol or a dialkyl ether that has at least one tert-alkylgroup, in a molar ratio of complexing agent to boron trifluoride of 2 to1.25:1.
 17. The process as claimed in claim 15, wherein thepolymerization reaction is conducted in the reactor at a residence timeof from 5 seconds to several hours at a temperature ranging from 0 to−30°C.
 18. The process as claimed in claim 17, wherein thepolymerization reaction is conducted in the reactor at a residence timeof from 1 to 30 minutes at a temperature ranging from −5 to −25°C.